Computer systems, including desktop, portable computers, may operate in a power saving mode of operation in order to reduce power consumption. One such power saving mode of operation may be referred to as “sleep mode.” A computer system may be invoked to enter a sleep mode of operation after a period of inactivity or upon a user invoking the computer system to enter the sleep mode of operation. Upon entering the sleep mode of operation, the state of the system may be stored in volatile memory, e.g., Random Access Memory (RAM). For example, register contents storing system state information may be stored in volatile memory during the sleep mode of operation. The “sleeping” computer system may be “awakened” or resumed upon an event such as a user's keystroke, receipt of electronic mail, a fax, etc. That is, upon an awakening event, the computer system exits out of the sleep mode of operation and resumes a normal mode of operation.
Another power saving mode of operation may be referred to as “hibernation.” A computer system may similarly be invoked into hibernation as invoking the sleep mode of operation. However, upon entering hibernation, the computer system stores the contents of the system state information in a non-volatile storage unit, e.g., disk drive, flash Read Only Memory (ROM), as opposed to storing the system state information in volatile memory. A computer system operating in hibernation may similarly be awakened as awakening the computer system operating in sleep mode.
A disadvantage of a computer system operating in hibernation than in sleep mode is that it takes longer for the computer system to enter a normal mode of operation. As stated above, the system state information may be stored in a non-volatile storage unit during hibernation. Upon the computer system operating in hibernation being awakened, the system state information must first be reloaded into volatile memory involving latencies such as mechanical latencies for hard drive accesses. In contrast, the computer system operating in sleep mode may resume normal operation faster since the system state information is already stored in volatile memory.
However, a disadvantage with storing system state information in volatile memory in sleep mode is that the information may be corrupted or lost upon occurrence of a memory corruption event, e.g., power outages, brownouts, power surges. As volatile memory requires continuous power to hold data, any data contained in volatile memory may be corrupted or lost during a memory corruption event such as a power reduction, however fleeting the power loss may be.
Since a computer system operating in sleep mode may resume to a normal operating mode faster than a computer system operating in hibernation, it would be desirable to enter the sleep mode of operation as a power saving mode of operation. However, as stated above, system state information may be corrupted or lost upon occurrence of a memory corruption event during sleep mode.
It would therefore be desirable for a computer system to be able to enter a normal mode of operation from a sleep mode of operation without any corruption or loss of data if a memory corruption event, e.g., power outages, brownouts, power surges, occurs.